1. Field of the Invention
The present invention relates to a piezoelectric element for use in a piezoelectric injector.
2. Description of the Related Art
The piezoelectric element utilizes the piezoelectric effect of a piezoelectric material, and since it has a high response speed and uses no mechanical components, the piezoelectric element is used as an actuator in various fields. For instance, an injector utilizing the piezoelectric element has been developed for use, instead of a solenoid which utilizes an electromagnetic force, in driving a fuel injector to open or close in an internal combustion engine of an automotive vehicle. FIG. 12 shows a piezoelectric element connected to a driving circuit. The piezoelectric element 91 has a laminated body 91a in which piezoelectric layers 911 and internal electrodes 912 are alternately laminated, whereby the piezoelectric element 91 is constructed so as to be displaced by applying a voltage between the internal electrodes 912. The application of the voltage to the piezoelectric element 91 is implemented from a current source 921 for the driving circuit 92 which is constituted by a capacitor or the like via external electrodes 914 formed on side surfaces of the laminated body 91a.
Over-charging the piezoelectric layers 91 may cause, immediately the piezoelectric layers 911 are charged, an elongation thereof which is greater than required, leading a failure of the piezoelectric layer 911. To cope with this, an inductor 922 is provided in series with the piezoelectric element 91 at an intermediate position along the length of a line 93 for suppressing the over-charging of the piezoelectric layers. However, it is necessary to avoid the interference, by the inductor utilizing electromagnetic induction, with other coil components or the like, and this imposes a limitation to the layout of components in the driving circuit, thus there is no way to prevent the enlargement of the driving circuit. Moreover, especially in the event that the number of inductors increases as the number of piezoelectric elements does, as seen in a case where a plurality of piezoelectric elements of different specifications are driven, the driving circuit 92 becomes larger.
The present invention was made in view of the aforesaid situation, and an object thereof is to provide a piezoelectric element which can be driven with a small and simple driving circuit.